"Protesters used slingshots loaded with marbles and stones to fire at police, injuring many officers," he said.

"Police saw the situation escalating, so they decided to use teargas."

Tens of thousands of rubber farmers demonstrated against steep falls in prices earlier this month, blocking roads and railways, in one of the biggest challenges against the populist government of Prime Minister Yingluck Shinawatra.

Finance Minister, Kittirat Na Ranong, has said the government will not renegotiate the rubber subsidy.

The farmers who oppose the government's deal say if their demands are not met within a week they will take their protest to the parliament in Bangkok.